Bipolar Molecules with Hybridized Local and Charge-Transfer State for Highly Efficient Deep-Blue Organic Light-Emitting Diodes with EQE of 7.4% and CIE_y ∼ 0.05

摘要

Donor-acceptor molecules with hybridized local and charge transfer (HLCT) excited state have been demonstrated to be an efficient strategy for achieving high performance electroluminescence by harvesting both singlet and triplet excitons. In this study, a series of bipolar D-A molecules with twisted bridge are synthesized and these chromophores exhibit good thermal, morphological and photophysical properties, electrochemical stabilities as well as HLCT excited state features. Excellent deep-blue electroluminescence (EL) performances are achieved using CSiTPI (external quantum efficiency (EQE) of 7.1% and CIEx,y coordinates of (0.16, 0.06) in a nondoped OLED) and DSiTPI (EQE of 7.4% and CIEx,y of (0.16, 0.05) in a doped OLED) as emitters with small full width at half maxima (FWHM, 45-48 nm). Devices using DSiTPI and CSiTPI as hosts are also fabricated and all the devices show high EL performances and small efficiency roll-offs. A green device with DSiTPI acquires maximum current, power, and EQE of 78.5 cd A(-1), 72.5 lm W-1, and 20.8%. The research demonstrates that excellent deep-blue EL performances with good color purity can be achieved using D-A emitters with highly twisted bridge in HLCT OLEDs.